That's terrible. I've seen a few people reporting that they got spooled. All that line in the water will be killing some birds and wildlife unfortunately.
I've thankfully yet to experience getting spooled, either in the river or the salt. I've certainly had Chinook take plenty of line and have to chase them downstream a bit, but never to the point I was seeing the bottom of my spool. Maybe I run my drag too tight, have definitely broken a few off. Is it just plain bad luck or anything one could do to avoid it? Seems like worst case could you not just point the rod tip straight at the fish and break it off at the leader like you would a snag, or does it happen too fast for that? Again, I can only speculate what the options would be, not having been in the situation.